Stability checkpoint stable-v1.0.19 (UI) — Phase B-7 wave delivered: 6 .scss splits (quality/customers/security/settings/diagnostic/about all thin @use chains) + 2 .ts splits (quality-types/diagnostic-types + customers data/helpers/types + customers-helpers spec). UI file-length hygiene: only dashboard still above 1000 LOC (deferred to Phase B-6 fresh session). Post-merge main pipeline #357 SUCCESS on bd9ca06.